net/mlx5e: Verify dev is present for fix features ndo

The native NIC port net device instance is being used as Uplink
representor.  While changing profiles private resources are not
available, fix features ndo does not check if the netdev is present.
Add driver protection to verify private resources are ready.

Fixes: 7a9fb35e

 ("net/mlx5e: Do not reload ethernet ports when changing eswitch mode")
Signed-off-by: Roy Novich <royno@nvidia.com>
Reviewed-by: Roi Dayan <roid@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>